1. Field of the Invention
The present invention relates to a signal processing system for processing a signal received from a mobile station, and a signal transmitted to the mobile station in wireless mobile communication systems including a GSM (Global System for Mobile Communications), a W-CDMA (Wideband-Code Division Multiple Access) system and the like.
2. Description of the Related Art
As connection configurations of a radio network controller (RNC) and a base transceiver station (BTS) in conventional mobile phone systems, one of the configurations of FIG. 1A through FIG. 1C has been selected and employed.
In the connection configuration of FIG. 1A, m number of BTSs BTS1 through BTSm are connected to an RNC 11 via an ATM (Asynchronous Transfer Mode) network 12. Each BTS comprises antennas (ANTs) 21-1 through 21-6, transmission/reception units (Transceivers) TRX1 through TRX6, a control unit (CP) 22, a surveillance unit (SV) 23, a base band unit (BB) 24, and an interface (I/F) 25. Each transmission/reception unit comprises a transmission unit (TX), a reception unit (RX), and a power amplifier (PA). The base band unit 24 comprises n number of base band signal processing units BB1 through BBn.
Each antenna 21-i (i=1, 2, . . . , 6) can transmit and receive four carrier signals C1 through C4 (of frequencies f1 through f4). Each carrier signal can use the maximum number of channels in the wireless mobile communication system of the GSM, W-CDMA or the like. Each base band signal processing unit performs base band signal processes in units of channels.
In the connection configuration of FIG. 1B, the BTSs BTS1 through BTSm are connected to an RNC 31 via an IP (Internet Protocol) network 32. Each BTS employs the configuration in which the interface 25 is replaced with an interface 33 in the configuration of FIG. 1A.
In the connection configuration of FIG. 1C, the BTSs BTS1 through BTSm are connected to the RNC 11 via the ATM network 12 similarly to the configuration of FIG. 1A. Each BTS employs the configuration in which the antennas 21-1 through 21-6 and the transmission/reception units TRX1 through TRX6 are removed from the configuration of FIG. 1, and is connected to the transmission/reception units TRX1 through TRX6 via an optical network 41.
The Patent Document 1 below discloses a technique of load distribution performed by causing the ATM network used by a wireless access network in a W-CDMA communication system to have functions of IP network.
Patent Document 1
Japan Patent Application Publication No. 2004-048209
The conventional connection configurations described above have the difference just of connection method between the base band unit and the transmission/reception unit i.e., the difference whether they are connected by the electrical connection or by the optical connection. Thus, in any of the above configurations, the channel resource capacity (the number of the channels) in units of antennas is limited by the number “n” of the base band signal processing units provided in the BTS. Accordingly, when there are connection requests from the mobile stations in the larger number than the presumed channel resource capacity, communications with some of the mobile stations have to be disconnected because of lack of resource.